A method for printing on paper is known, for example, from US patent publication US 2005/0062819. In this known method, an ink fluid, which contains at least one water-soluble dye and a dispersion of resineous microparticles, is applied to a paper substrate. Additionally, a colourless ink, containing at least one resin, is used on at least a part of the substrate. The colourless ink preferably contains a resin, water-soluble solvents and water as the main constituent. Preference is for resins which are insoluble in water. The quantity of colourless ink which is applied to the paper is dependent on the quantity of dye-containing ink fluid which is applied. The quantity of colourless ink is preferably applied only to parts of the paper where no dye-containing ink fluids have been/are applied. In those areas where dye-containing ink fluids are printed, little or no colourless ink is applied. With this known method, it is intended to realize a range of objectives including, in the first place, the combating of colour deterioration resulting from the presence of harmful gases such as ozone by the sealing of the substrate surface, and, in addition, the reduction of gloss differences, the elimination of after-treatments such as heating, pressing or light irradiation, as well as the prevention of a reduction in image quality caused by ink leakage, etc.
When a substrate is printed on with the aid of an inkjet printing device, the image quality can generally be improved by applying a receiving layer to that print side of the substrate which is to be printed on. This receiving layer is composed such that the ink fluid, virtually immediately after the application, is retained in the receiving layer on the print side of the substrate. Thus, an improved colour density can be achieved, as well as an enhanced image sharpness. Accurate dosing and positioning of the ink drops of the ink fluids in order to achieve the correct sharpness and combat disturbances of the print images, for example as a result of so-called Moiré effects, are generally necessary. This applies to both textile substrates and other, for example, paper (cellulose)-based substrates.
In addition to these general requirements with regard to colour density and image sharpness, there are image quality requirements which are of greater or lesser importance, depending on the application of the printed substrate.
The evenness of colour gradients is one of these requirements. In a so-called colour wedge (saturation gradient of a colour), colour gradients, in particular differences between two neighbouring colours (also referred to as colour steps), must be as little visible as possible. In order to achieve this, according to the prior art, in addition to the basic colours K (black), C (cyan), M (magenta), and Y (yellow), the lighter variants of these colours are used, i.e. LK (light black or grey), LC (light cyan), LM (light magenta) and LY (light yellow). The colour impression is determined by the integral colour seen by the naked eye over a defined limited area. If a light colour has to be printed using ink fluids with a high density of the dyes, this implies that the drops must be deposited relatively far apart on the substrate in order to give the correct colour impression. The mutual spacing can then be of such magnitude that the drops are separately distinguishable in the form of granularity. The light variants of the basic colours are used to suppress this granularity.
The drawback of such a choice comprising an extended set of colours is that the used inkjet printing device needs to possess just as many ducts and nozzles in order to be able to make use of the full colour space covered by these basic colours and light variants thereof. When printing on a textile substrate, the use of just the basic colours K, C, M and Y often produces too limited a colour space. In order to further extend the colour space, additional colours are therefore used, such as red (R), blue (B), orange (O) and golden yellow (GY). These additional colours, in an inkjet printing device having the very same number of (typically, for example, 8) ducts and nozzles, are detrimental to the light variants of the basic colours. It may be concluded that, according to the prior art, only compromises are possible, limitations being placed upon the colour space and evenness in respect of an inkjet printing device with a given configuration.
So-called interlacing is likewise used with a view to improving the image quality. Interlacing is the construction of a picture element by the use of a plurality of different jets for each colour in order to equalize differences in jet position and drop size between different jets. By virtue of this technique, striping (i.e. visible appearance of dark or light lines parallel to the motional direction of the print head) and Moiré effects (patterns visible with the naked eye, which are caused by small differences in positioning in grids of printed drops) are suppressed. The degree of interlacing is inversely proportional to the productivity of the used printing device, which can be a drawback. After all, the print head, in order to produce a picture element with the same quantity of ink, must address the same picture element more often. The positions at which the drops exactly make contact with the substrate is primarily dependent on the accuracy of the physical zero point of each printing stroke. In addition, the positions are also dependent on the motional direction and speed of the print head in relation to the substrate. In so-called bidirectional printing, the print head prints both during the forward motion from right to left and in the return motion in the reverse direction. As a result thereof, the drop jet has in both cases an opposite lateral speed in relation to the substrate. Displacements of drop patterns in the order of magnitude of just a quarter of a picture element in relation to a previous stroke cause already with the naked eye visible differences in colour impression. The differences in positioning of the ink drops between two different strokes cause a density difference between the two printed bands as a result of the drop patterns of one stroke just overlapping or just failing to overlap with the drops of the previous stroke. Especially in surfaces with one and the same colour, bands are then visible, which is also referred to as colour banding.
In GB2356955 system is disclosed in an inkjet printer for determining the amount of a fixer to be applied to a medium. Fixers may be a clear solution or may even be dye-based ink printed beneath a pigment-based ink. Fixers allow inks to bond to a medium thereby improving edge sharpness. Fixers also help increase the drying speed of inks and improve water fastness. Use of a transport fluid or auxiliary fluid is not disclosed.
According to US2003/0081094, thermal inkjet printheads and piezoelectric printheads may be connected to separate ink supplies to thereby enable each of the printheads to eject fluids (e.g., dyes, pigments, undercoats, over-coats, etc.) having various characteristics onto a recording medium. Examples of the various characteristics of the fluids may include, color, viscosity, pigment content, and the like. Again, use of a transport fluid or auxiliary fluid is not disclosed.
The object of EP1391301 is to provide an ink jet recording method and ink set with which recorded material with excellent gloss and greatly reduced gloss unevenness can be obtained, in which a pigment ink composition and a clear ink composition containing a resin component are discharged to record information on a recording medium, wherein the discharge amount of the pigment ink composition and/or the discharge amount of the clear ink composition is adjusted so that the gloss will be substantially uniform over the entire recording surface of the recording medium after recording.
US2002/0054196 concerns an image forming apparatus and image forming method. Use is made of a controlled amount of a diffusion liquid. Diffusion liquids are liquids which are capable of decreasing the density of ink by spreading the ink on a print material in a planar direction thereof. An example of a diffusion liquid is a liquid which thins ink, such as an organic solvent or transparent, colorless water not including dye or pigment. A diffusion liquid which has less wettability than the ink used with respect to the sheet 4, serving as a print material, that is, a diffusion liquid which does not spread on the sheet 4 more than is necessary when it is adhered thereto and which exists in liquid form for a long period of time is selected. In addition, the diffusion liquid which is selected has excellent wettability with respect to the ink used. Use of a transport liquid is not mentioned.
From US 2006/0087540 A1, a method for printing on textile with the aid of an inkjet printing device is known, wherein the ink fluid comprises a disperse dye, a dispersing agent and a water-soluble organic solvent, and the textile substrate is pre-treated with an organic acid, the pH of which is lower than the pH value of the ink fluid. With this method, it is intended to result in no waste sludge and to improve the washing characteristics of the printed substrate.
Textile printing with the aid of an inkjet printing device has per se a further number of supplementary requirements which are specifically related to the application in question.
For example, in the printing of flags, so-called through-printing needs to be achieved, so that both sides of the substrate display a comparable image. This is comparable with conventional screen printing, in which the printing paste is pressed through the cloth. In the one-sided printing with the aid of an inkjet printing device, for this a contactless transport of dye is necessary from the print side of the substrate to the opposite-situated side. If an extra quantity of ink is delivered in order to saturate the cloth and thus achieve through-printing through the substrate, a heavy and uncontrolled spreading of ink fluid may occur, which is a negative side effect. The end result can then be unsatisfactory in terms of colour value and image sharpness.
In textile printing intended for the manufacture of swimwear from high-stretch textile materials, such as a polyamide and polyurethane knitted fabric, for example polyamide Lycra, some penetration beneath the outer surface is required, without the need for full through-printing. After all, when the fabric is stretched, no uncoloured fibres must be visible. To this end, polyamide Lycra, for example, is printed with an ink fluid having within it a dispersed dye which, after the printing, under the influence of temperature and pressure diffuses in the fibres of the substrate. The flow of the dye around the fibre during the printing ultimately determines where the fibre in question is coloured. Too great a flow reduces the image sharpness of the print image. A limited flow provides a white transparency of the fibres when the printed material is stretched. It has been shown that, especially in light-coloured picture elements, flow is insufficient or totally unachievable with the techniques according to the prior art. The quantity of delivered ink is insufficient to realize the necessary depth transport or penetration.